Chapter 6 Notes: Olivia Ward

Formation of Planetary Systems: Our Solar System and Beyond

6.1 A Brief Tour of the Solar System
What does the solar system look like?

• The solar system exhibits clear patters of composition and motion.
• Large bodies in the solar system have orderly motion. All planets have circular orbits going in the same direction and nearly in the same plane.
• Planets fall into two major categories: small & rocky terrestrial planets and large, hydrogen-rich jovian planets
• Swarms of asteroids and comets populate the solar system. Vast numbers of rocky asteroids and icy comets are found throughout the solar system.
• Several notable exceptions to these trends stand out: some planets have unusual axis tilts.
• The Solar System
  
  • The Sun
    
    • Over 99.8% of the solar system's mass
    • Made mostly of H and He gas (plasma)
    • Converts 4 million tons of mass into energy each second
  • Mercury
    
    • Made of metal and rock: large iron core
    • Desolate, cratered, long & tall steep cliffs
    • 425° C during the day, -170° C during the night
  • Venus
    
    • Nearly identical to the size of Earth
    • Surface hidden by clouds
    • Hellish conditions due to an extreme greenhouse effect
    • Even hotter than Mercury: 470°C day and night
  • Earth
    
    • An oasis of life
    • The only surface of liquid water in the solar system
    • A surprisingly large moon
  • Mars
    
    • Looks almost like Earth
    • Giant volcanoes, a large canyon, polar caps
    • Water flowed in the distant past
  • Jupiter
    
    • Much farther from the Sun than the other inner planets
    • Mostly H & He, no solid surface
    • 300 times more massive than Earth
    • Many moons:
      
      • Io (active volcanoes all over)
      • Europa (possible subsurface ocean)
      • Ganymede (largest moon in the solar system)
      • Callisto (a large, cratered ice ball)
  • Saturn
    
    • Giant and gaseous like Jupiter
    • Spectacular rings
    • Many moons (including Titan)
    • Rings are not solid. They are made out of chunks of ice and rock.
  • Uranus
    
    • Smaller than Jupiter & Saturn, much larger than Earth
    • Made of H & He gas and hydrogen compounds
    • Extreme axis tilt
    • Moons and rings
  • Neptune
    
    • Similar to Uranus (except axis tilt)
    • Many moons (Triton)
  • Pluto
    
    • Much smaller than other planets (dwarf planet)
    • Icy, comet-like composition

6.2 Clues tot he Formation of our Solar System
What features of our solar system provide clues to how it formed?

• Two major planet types: terrestrial and jovian
• Swarms of smaller bodies
  • Many rock asteroids and icy comets populate the solar system
• Notable exceptions
  • Rotation of Uranus
  • Earth's large moon

What theory best explains the features of our solar system?

• Nebular Theory: our solar system formed from a giant cloud of interstellar gas (nebula = cloud)
  
  

6.3 The Birth of the Solar System
Where did the solar system come from?

• Galactic Recycling
  • Elements that formed planets were made in stars and then recycled through interstellar space (process repeats).

• Evidence from other gas clouds
  • We can see stars forming in other interstellar gas. (clouds lending support in the nebular theory)

What caused the orderly patterns of motion in our solar system?

• Conservation of angular momentum
  
  • The rotation speed of the cloud from which our solar system formed must have increased as the cloud contracted.
• Flattening
  
  • Collisions between gas particles in the cloud
  • The spinning cloud flattens
• Disks around other stars
  
  • Observations of disks around other stars support the nebular hypothesis

6.4 Learning from Light
Why are there two major types of planets?

• Planets fall into two major categories:
  
  • Small: rocky terrestrial planets
  •  Large: hydrogen-rich jovian planet

•  Formation of terrestrial planets
  • Small particles of rock and metal were present inside the frost line.
  • Planetesimals of sock and metal built up as these particles collided.
  • Gravity eventually assembled these planetesimals into terrestrial planets.
• Accretion of Planetesimals
  
  • Many smaller objects collect into just a few large ones.
• Formation of jovial planets
  • Ice could also form small particles outside the frost line.
  • Larger planetesimals and planets were able to form.
•  Asteroids and Comets
  • Leftovers from the accretion process
  • Rocky asteroids inside frost line
  • Icy comets outside frost line
• Heavy Bombardment
  
  • Leftover planetesimals bombarded other objects in the late stages of solar system foundation.
• Origin of Earth's Water
  
  • Water may have come to Earth by way of icy planetesimals from the outer solar system.

How do we explain the existence of our Moon and other exceptions to the rules?

• Captured Moons
  
  • The unusual moons of some planets may be captured planetesimals (irregular shaped).
• Odd Rotation
  
  • Giant impacts might also explain the different rotation axes of some planets

When did planets form?

• 4.6 billion years ago
• Radioactive Decay
  
  • Some isotopes decay into other nuclei
    A half life is the time for half the nuclei in a substance to decay.